Marine Carbonate System Sensors

NOC has developed an integrated microfluidic lab-on-chip sensor for autonomous high-quality pH measurements onboard autonomous platforms. It utilises the standard spectrophotometric analytical method using meta-Cresol purple offering high accuracy (<0.005) and precision (<0.001) measurements for ocean acidification and ocean carbon cycle research.

It can be deployed for periods of longer than a year on autonomous platforms measuring at a maximum frequency of <6 measurements per hour. It has low power consumption and can be powered by either on-board batteries or an external power source. High performance electronics and communication systems allow on-board data processing and output of temperature and salinity corrected pH measurements. Pressure tolerant components allow deployments at a depth of 6,000 metres.

The pH sensor has been deployed around the world, including for coral reef studies, CCS storage site monitoring, long term pH monitoring in Germany, and on autonomous vehicles.

Current Specifications

Sample rate: 8 minutes   
Calibration method: Self referencing   
Precision: 0.002 pH units   
Accuracy: 0.005 pH units   
Sample volume: 400 µL per measurement   
Deployment depth: to 6000 m   
Voltage range: 10 V to 16 V   
Power consumption: 1.8 W   
Current draw (12 V): 155 mA average, 385 mA maximum   
Output interface: RS232, USB   
Connector type: SubConn MCIL8M   
Dimensions: 17 cm long, 15 cm diameter (without reagent housing) 56 cm high, 20 cm diameter (sensor with reagent housing)   
Weight in air: 3.6 kg (without reagent housing) 6 kg (sensor with reagent housing)   
Weight in water: 0.85 kg

This sensor uses lab-on-a-chip technology to sample seawater and perform single-point open-cell titration with an optical measurement. It can carry multiple calibration materials on board, allowing for routine recalibration and quality checks in the field. The sensor has been characterized in the laboratory and in a pressure testing facility to 600 bar (equivalent to 6 km depth) and deployed in estuaries and coastal environments, ship’s underway systems, landers, moorings, and on remote-operated and autonomous underwater vehicles. The sensor has a field-demonstrated precision and accuracy regularly better than 5 μmol kg–1 and a sample time of ~10 minutes.

Current Specifications

Sample rate: 10 minutes   
Calibration method: Self-calibrating to on-board reference materials in the field 
Precision: <5 umol/kg   
Accuracy: <5 umol/kg   
Sample volume: 3 mL per measurement   
Deployment depth: to 6000 m   
Voltage range: 10 V to 16 V   
Power consumption: 1.8 W   
Current draw (12 V): 155 mA average, 385 mA maximum   
Output interface: RS232,USB   
Connector type: SubConn MCIL8M   
Dimensions: 17 cm long, 15 cm diameter (without reagent housing) 56 cm high, 20 cm diameter (sensor with reagent housing)   
Weight in air: 3.6 kg (without reagent housing) 6 kg (sensor with reagent housing)   
Weight in water: 0.85 kg

The DIC sensor uses lab-on-a-chip technology to sample seawater and perform a conductometric measurement of DIC.  The sample is acidified to convert all the DIC content into dissolved gaseous carbon dioxide (CO2), which is then pumped through a unit containing a gas-permeable membrane where the CO2 diffuses through to an acceptor solution on the other side.  The resulting conductivity change of the acceptor solution provides an indirect measurement of DIC content within the sample. 

The sensor has been characterized in the laboratory and in a pressure testing facility to 600 bar (equivalent to 6 km depth) and deployed in estuaries, ship’s underway systems, and on remote-operated vehicles.

Current Specifications

Sample rate: 10 minutes   
Precision and accuracy: in development 
Calibration method: Self-calibrating to on-board reference materials in the field 
Deployment depth: to 6000 m   
Power, size, and weight are similar to the pH and TA sensors.